Patent GB-417057-A (GB)
Title: Improvements in or relating to very short wave radio communication systems
IPC: H01J25/68
Filed: 1933-03-23
Abstract: 417,057. Wireless signalling; valve amplifying, generating, and modulating circuits. MARCONI'S WIRELESS TELEGRAPH CO., Ltd., Marconi House, Strand, London.- (Assignees of Lindenblad, N. E. ; Port Jefferson, Long Island, New York, U.S.A.) March 23, 1933, No. 8839. Convention date, April 5, 1932. [Class 40 (v).] The invention comprises a system for signalling on wave-lengths of the order of centimetres, utilizing frequency-multiplying and modulating valves in which the electron stream is subjected to a steady magnetizing-field, and in which the plate, grid, and cathodeheating circuits are tuned by means of Lecher wires. The valves may be used as single or push-pull frequency-multipliers and amplifiers, and as amplitude, frequency, or phase modulators. Means are also described for stabilizing the generated frequency ; for maintaining the voltage supply to the signalling system at a constant value in spite of load variations ; and for relaying short-wave signals from point to point so as to extend the effective range beyond the optical limit. In the complete transmission system shown in Fig. 1 (Sheets 1 and 2), a pair of master oscillators MO, (sheet 1) are connected through Lecher-wire couplings C to the filament circuit of a buffer amplifier BA, and then through similar couplings Cl to a magnetic frequencymultiplier MFM, (sheet 2), from which the stepped-up frequency passes through an absorption circuit AS and coupler C2, on to a transmission line TL feeding the unidirectional aerial system TA. Amplitude modulation is effected at MM by signal frequencies fed through a low-frequency amplifier AA. The voltage supply to the electrodes of the various valves is maintained constant by a voltage regulator VR1, described subsequently. The tuned grid circuits 6 of the master oscillator system MO are grounded through a resistance 24 from a bridge-strip 22; the anode circuit 8 is tuned by trombone slides 30, 32; whilst the filament leads pass through tubes 52, 54 to an earthed tuning strip 60, the high-frequency currents flowing through this circuit in parallel. A long-line frequencycontrol circuit 70, 72, 74 is connected to the tuned filament circuit at points 66, 68 and is bridged at intervals, as shown, the centre impedance or resistance 78 preventing " odd " multiple half-wave jumps in frequency, whilst the resistance 76 prevents similar " even " wave-length variations. The output from the buffer amplifier BA is fed through coupling lines 132, 134 to the anodes 140, 142 of the magnetic frequencymultiplier MFM, back-feed of the generated harmonic frequencies being prevented by making the connections to voltage nodes on the tuned anode circuits 136, 138, which may be grounded at 158. The output or grid circuit 160, 162 is tuned to an harmonic of the applied frequency (i.e. to 450,000 K.C. for an input of 150,000 K.C.) and is grounded through a grid-biassing resistance 192. The cathode circuit is tuned as before by a strip 174. A magnetic field is applied across the valveelectrodes by a pair of solenoids 180, 182 wound in series and joined by a magnetic yoke 184. They are energized from a source 42 through a variable resistance 188. The valves are so biassed by the leak resistance 172 that " peaks " of the input voltage cause spurts of electrons to impinge upon the grids, from a "reservoir" of free electrons formed by the magnetic control in the space between the cathode and grid. This is stated to enhance both the volume and speed of the electrons reaching the grid, thereby facilitating the formation of harmonic frequencies in the output. The harmonic output from the magnetic frequency multiplier MFM is fed through condensers to a trombone-tuned absorption circuit AS, which is coupled to the grid of a magnetic modulator MM at voltage nodes 202, 204. The anodes 230, 232 of the modulator are in this case left "floating." Signal voltages are applied to the grid from the amplifiers AA, together with a biassing voltage, from a resistance 244, and modulate the carrier frequency by causing more or less energy to be shunted away from the absorption circuit AS. The transmission line TL follows the construction described in Specification 379,796. The aerial comprises parallel half-wave radiators 278, with crossover connections, backed by a plane metallic reflector 272, spaced a quarter wave-length away. All the radiators are energized from a common supply line 274 which is short-circuited at both ends. The aerial may be tilted upwards towards a reflector mounted at the top of a tower some 500 feet high, in order to increase the normal "optical" range of transmission ; a similar system is arranged at the point where the first beam touches the earth's surface, and so on. Or the signals may be directly relayed from one to the other of a series of bilateral directive aerials. Fig. 5 shows the tuning conditions in the input and output circuits of a typical push-pull combination in simplified form, the capacity between the plate and grid serving as an impedance transformer as shown in dotted lines. The voltage for the various valves is regulated at VR1, Fig. 1 (Sheet 1) as follows : Any increase in the supply voltage from the source 88 raises the grid bias applied to the regulating valve 80 from a resistance 96, which is inserted between the supply lead 92 and a reversed source of potential 98. This in turn causes more current from the anode of the valve 80 to flow through the resistance 100, and so stabilizes the voltage of the point Y to which the anodes of the master oscillators and amplifiers are connected. A similar voltage regulator VR2 controls the supply to the buffer amplifier tubes 106, 108. In a modified arrangement shown in Fig: 2 a crystal-controlled master oscillator 300 feeds the tuned cathode circuit 304 of a second master oscillator LMO and stimulates it into oscillation at a frequency which is "locked" with that of the generator 300. The output is fed first to a magnetic frequency-multiplier MFM and then into an absorption circuit AS, to which the modulating systems MM and AA are coupled as shown. Grid bias for the modulator MM is derived from a resistance 366 connected to a strip 368 bridging the absorption circuit AS. The grids of the modulators MM are connected to the same circuit through leads 402, 404, to which the LF amplifier AA is also connected by a bridge-strip 400. A further strip 403 prevents back-feed. The modulated signal energy is radiated from an aerial TA of the kind described in Specification 346,023. In an alternative system the microphone signals are applied through a choke coil to the grid-cathode circuit of the modulator (Fig. 4, not shown). The invention is also applied to single instead of push-pull valve circuits, the anode and cathode in this case being tuned in identical fashion. Frequency modulation may be effected by varying the voltage on either the grid or anode of the magnetic frequency multiplier or master oscillator, or by varying the field intensity of the control solenoids. Specification 358,264 also is referred to. In the Specification as open to inspection under Sect. 91 a split-anode frequency-multiplier 618, Fig. 9 (Cancelled) is used for phase modulation. Carrier oscillations from a crystalcontrolled generator 600 are supplied to modulating valves 604, 606 through an inductive reactance 608 and a capacity reactance 610 respectively. Signal energy is simultaneously fed to the screen grids of these valves in phaseopposition from a transformer 608<1>. The resultant constant-frequency phase-shifted output passes through a frequency-multiplier 614 to a magnetic frequency-multiplier 618 having trombone-tuned circuits connected across the pair of split anodes 622, 624, the output circuit 634 being tuned to an harmonic of the circuit 616. Specifications 318,619, [Class 40 (v)], and 373,692 are referred to. This subject-matter does not appear in the Specification as accepted.